During the 1980's, a means of suspending a prosthesis was developed which consisted of a docking means fabricated into an interface which, in turn, was rolled onto the distal portion of the wearer's residual limb. The docking means engaged into the prosthesis, and the prosthesis was thereby locked in position of attachment to the patient's limb.
Such a means of attachment became standard in the industry. However, it had drawbacks which ultimately led to its supplantation by other methods. One major drawback was the tendency of the residual limb to piston, or slip upwards and downwards in the interface upon ambulation. Over the years, it has been thought that pistoning occurred because only the distal portion of the limb was involved in the support of the prosthesis. The limited support resulted in a high degree of angular and torsional stress at the interface of the socket/liner and the residual limb. The pistoning, in combination with the sucking effect caused by the interface, caused the limb to change in volume with ambulation. As a result, the fit of the prosthesis changed with wear throughout the day. It was necessary for the wearer to make use of a thick prosthetic sock on the residual limb in an attempt to compensate for the limb's change in volume during use of the prosthesis and alleviate some of the discomfort which was experienced as a result of pistoning. However, the sock added an inconvenient bulk to the already awkward task of wearing a prosthesis, as well as creating sanitary issues due to the collection of sweat and dirt.
In the 1990's, suspension sleeves were used as an interface to create a seal between the residual limb and the prosthesis. The suspension sleeve is an elastic or elastomeric tube which, when properly positioned, forms a seal which encompasses 1) the proximal lip of the prosthesis socket, 2) the entire portion of the interface external to the socket, and 3) a portion of the wearer's thigh just above the proximal end of the interface. Such a prior art sleeve, employed in its sealing capacity, is illustrated in FIGS. 1 and 2. The seal created by the elastomeric sleeve is able to support a modest vacuum. The vacuum is typically in the range of from greater than about 2 inches Hg to about 14 inches Hg. One way valves embedded in the prosthesis socket/liner or pumps are often used to establish and maintain the vacuum.
The sealed socket limb junction of these prior art prostheses largely eliminates the pistoning problem. Furthermore, such prior art prostheses included a layer of fabric or other porous or continuously cavitated compressible material such as, for example, a synthetic foam, which overlies the entire interface and occupies an area between the socket and the interface, and serves to “wick” the vacuum to the entire volume occupied thereby, yet it prevents the interface from coming into contact with the socket, effectively establishing a volume over which a vacuum can be sustained.
However, this method introduces new problems. The upper reaches of the seal extend onto the thigh of the wearer, essentially including the skin of the wearer in the partially evacuated volume. The skin directly under the sleeve chafes from the elastic motion of the sleeve as the residual limb compresses and decompresses with the ambulation cycle. Furthermore, bending at the knee causes the sleeve to bunch directly behind the knee and on the back of the leg above the knee, and stretch tightly in the analogous positions on the front of the residual limb. Such motion can cause blistering and subsequent infection and pain, even to the extent of requiring the wearer to forego the use of the prosthetic for periods of time. Nevertheless, the sealing of the partially evacuated volume by extending the sleeve to the wearer's thigh, and the inclusion of the wearer's skin as a bounding surface to the partially evacuated volume have persisted as part of the solution to the pistoning problems arising from earlier designs.
A prosthetic liner system surmounting the foregoing problems associated with the thigh-sealing liner system, yet maintaining the effectiveness against pistoning demonstrated by the thigh-sealing liner system would represent an advance in the prosthetic liner industry.